In recent years, flexible electronics have gained popularity with various applications ranging from flexible displays, wearable electronics and ID tags, and biomedical devices, to structural health monitoring. These applications in general do not require the use of very high speed devices, but the flexibility of the electronics is of critical importance. Typically, these low speed flexible electronics are based on organic or low temperature deposition-compatible amorphous semiconductors (e.g., Si) or metal oxide materials, which can be processed with large area printing, coating, and deposition techniques. Among them, roll-to-roll production is one of the most desirable fabrication methods, offering the benefits of high throughput and low cost. Several key steps in the process, such as patterning and thin-film deposition, have been successfully demonstrated on flexible substrates. In addition, some research groups have demonstrated active components with reasonably good DC performance using organic semiconductor materials. However, the devices reported operate at relatively low frequencies due to the low mobility of the semiconductor materials.
Radio-frequency (RF) capable transistors, due to their wider signal handling capability, can extend printed electronic applications toward RF data transmission and wireless power transfer or allow circuits to operate with lower power consumption. The main challenges in this pursuit include: (1) a lack of materials with sufficient mobility; and (2) difficulties in defining a fine channel region using a scalable fabrication process. Although several RF capable flexible field-effect devices fabricated using nanowires have been reported, the approach cannot be adapted for mass production. Furthermore, conventional nanoscale patterning techniques, such as e-beam lithography, cannot meet the requirements for mass production on flexible substrates.